Orbital Insertion and Space Combat Tactics – Part 4

One issue that is almost universally ignored in science fiction these days is the role of orbital mechanics in space combat tactics. Science fiction space combat tends to be written or visualized as if the spacecraft involved have nearly infinite energy and thrust available. Occasionally this is due to the writers or visual effects technicians consciously simplifying things for viewers. Unfortunately, however, most of the time it’s simply due to the writers being woefully ignorant of the subject.

In Part 1 we showed that any reasonable account of space combat in near-to-medium-future hard sci-fi must account for orbital mechanics. In Part 2 we discussed that pros and cons of higher orbits and lower orbits. In Part 3 we examined cases where our two spacecraft occupied dissimilar orbits. In our final part, we’ll discuss various considerations related to actual maneuvering between orbits.

As we noted back in part 1, the fundamental reason that we must consider orbital mechanics is the massive energy requirements necessary for raw point-to-point travel in space. Current technology and technology that can be extrapolated from known and proven physics are not capable of breaking past these limits. This same factor imposes limits on orbital maneuvering.

There are three fundamental factors that will drive maneuvering of combat spacecraft: mass, thrust, and fuel. All three of these factors are intrinsically related. More fuel means more mass. More mass requires more thrust to move it. More thrust requires more fuel.

At the same time, there are unavoidable trade-offs in modern propulsion technology. To put it bluntly, the more efficient a propulsion method is, the less thrust it produces. Solar sails and ion drives are highly efficient, but they produce low thrust. This makes them possibly great for long distance travel but very poor choices for the quick maneuvering desired by military vessels.

It seems likely that military craft will mostly rely on such non-chemical propulsion for major drive components (ie, for interplanetary travel). Nuclear power seems a particularly likely choice, just as it is on today’s major naval vessels – and for the same reasons. Nuclear power is very efficient, providing quite a bit of energy for a given fuel mass. Unlike many other propulsion sources, however, it can also provide high thrust. This allows for relatively short transit times, such as military vessels will require.

However, even nuclear propulsion is likely to be poorly suited for fast maneuvers. It is highly likely that chemical rockets will be used for maneuvering thrusters. Based on known technology and physics, quick maneuvering is likely to stay the domain of chemical rockets for some time – and chemical rockets require lots of fuel. Lots of fuel means lots of mass. It also means that the spacecraft must be very careful in how that fuel is used, because once it’s gone it’s gone.

A further consideration is that large drive engines also have great potential to be used as weapons – especially nuclear propulsion engines. This was the second reason that the battleships described in “The Fourth Fleet” had main drive engines both fore and aft. This allowed the ships to use them not just for propulsion but also as the main weapon system. An important consideration, however, is that use of this weapon system will also impact the navigation of the vessel itself.

It is also worthy of note that the design choices described herein will be hugely expensive, thus likely limiting this kind of vessel only to major spacefaring powers. As with modern navies, lesser powers will be forced by economics to limit themselves to less expensive military spacecraft. And also much like the world of today, these vessels are extremely unlikely to be common among private owners.

In Part 1 we showed that we must account for orbital mechanics. In Part 2 we discussed orbits of differing altitude and velocity. In Part 3 we’ve discussed retrograde orbits and non-aligned orbits. Here in Part 4 we discussed maneuvering itself in more detail and also discussed some ways in which this will impact spacecraft design.

This series is the beginning of the discussion, not the end. Any discussion that takes place before such warfare is necessarily speculative. Yet we already know many factors that must effect the discussion. Though this discussion will continue for decades and centuries after space warfare becomes common, we are well served by beginning it now.

Orbital Insertion and Space Combat Tactics

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